This step-down regulator was found in the December 1985 issue of Radio Electronics magazine. The circuit has an input voltage of 25V.
Old multimeters used a 22.5 V battery for high resistance measurements. If you have one, you...
This circuit has an opposite action to the previous one, triggering when light falls on the...
This circuit was found in a Popular Electronics from 1991. The transistor could be the BC548. The...